s800NFSA Noise Lna

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SA 308: SA EnhancementsNoise Figure Lab

Noise Figure Lab S800 November 2003

ESA-E Series, Option 219

1

Agilent ESA Series Spectrum Analyzers

Option 219 -Noise Figure Measurements Personality and Hardware

Overview:

A key measurement in the development of devices and systems is its noise figure; considering

that this figure of merit is one of the key limiting factors in the overall systems performance. The

ability to make accurate noise figure measurements have significant financial benefits since aproduct with a guaranteed low noise figure commands a premium price. A manufacturer can

however only claim this reward, if every unit manufactured can be shown to meet its

specification.

Noise Figure Measurements are required in production to essentially demonstrate thatthe product meets its specification needs.

For the upstream customer interested in the low noise figure component; perhaps the system

integrator who is putting together a receiver, noise figure measurements is also of interest. Theywant to confirm that they are getting the performance that they have paid a premium for, and itwill indeed meet their design needs.

Noise Figure Measurements are required downstream for customers to confirm thatthey are getting the performance that they have paid for.

The engineer also has a choice to ignore this important parameter and instead over design the

other aspects of their communications link.

a) They can raise the transmitted signal power. This usually translates to a more costlydesign in terms of engineering time spent, or higher rated components. For the case of a

satellite, where the transmitter needs to generate large wattages at the frequenciesrequired, amplifiers fabricated via the regular chip process are no longer adequate. The

adoption of high power amplifiers like klystrons or magnetrons are required which are

orders of magnitude larger than the regular microchip PAs (BJTs, FETs). This translates

to a huge investment in paying the Boeings, Ariannes, Lockheed Martins, Lorals or

Northop Grummans of this world to send the larger payload into space.

b) Another way is to increase the amount of power, that the receive antennas intercepts.This translates to a larger receive antenna aperture size which after a while becomes

impractical because of environmental issues and other government regulations.

Measuring and then minimizing the noise generated in the components of your communications

system, is the alternative and recommended approach. Particularly, considering that approacheslike amplification and improving directivity has the same effect on the signal as on the noise.

Agilents noise figure measurement systems are an easy to use set of tools that automate

these measurements, providing high accuracy to meet many of your customers needs at avastly reduced cost.


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Fundamentals of noise figure measurements: There is not enough time to go through the intricacies of a

noise figure measurement so only a summary of equations relevant to the understanding of how a

measurement is made will be shown.

Fig 1: Theory refresher 1

DUTN

1=kGB(T

c+T

e)

N2=kGB(Th+Te)

GZs@TeZs@Th

Zs@TcY FACTOR

Y=1

2

N

N=

NaKTcBG

NaKThBG

+

+=

KTeBGKTcBG

KTeBGKThBG

+

+=

)(

)(

TeTcKBG

TeThKBG

+

+=

)(

)(

TeTc

TeTh

+

+

Y=mX+C

YTc+YTe=Th+Te Te(Y-1)=Th Ytc

Te= 1

Y

YTcTh

(1)

Na =Added Noise generatedin D.U.T.

N1 = Noise Power levelwith noise source on

N2 = Noise Power levelwith noise source off

Output Noise Power

N1

Na

N2

TsThTcTe

Temperature of

Source Impedance

F (Noise Figure) =

GKTsB

NaGKTsB

GNi

NaGNi

)GNiNa(GSi

NiSi

NoSo

NiSi

+=

+=

+

=

F (Noise Figure) =Ts

)TeTs(

GKTsB

)TeTs(GKB

GKTsB

GKTeBGKTsB +=

+=

+

F (Noise Figure) =Ts

)TeTs( + FTs=Ts+Te FTs-Ts=Te

Te=Ts(F-1) (2) from (1) Ts(F-1) =1

Y

YTcTh

Assume Ts=Tc TcF= Tc+1

Y

YTcTh

F = 1 +1Y

TcTcY

TcTh

=1Y

TcTcY

TcTh1Y

+

Rearranging F = 1 +1Y

TcTcY

TcTh

=

1Y

)1Tc

Tc(Y)1Tc

Th(

F =1Y

)Tc

TcTc(Y)

Tc

TcTh(

F =1Y

)Tc

TcTh(

ENR=)

Tc

TcTh(

F = 1Y

ENR

NF(dB) = 10Log (F) = 10Log ENR 10 Log (Y-1) (3)

So If we measure the Value of Y and we Tell the analyzer what the ENR is usually provided with

the noise source, then we should be able to measure the noise figure of the device under test.


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4

Lab 0. Setting up ESA

Switch to the noise figure measurement personality (Opt. 219).

Spectrum analyzers can make many different types of measurements. The noise figure personality is only

one of many modes that the ESA-E series can be operated in. This makes it a cost-effective way to expandthe capability of an essential engineering tool. If the ESA is not already in thenoise figure measurement

personality mode..

Instructions: ESA-E series SpectrumAnalyzer

Keystrokes: ESA-E series SpectrumAnalyzer

Switch to the Noise figure measurement

personality.

[Preset][Mode]({More 1 of 2} if necessary){Noise

Figure}

Lab 1. Entering the Excess Noise Ratio (ENR) Values

All demonstrations use the Agilent N4002A SNS Series smart noise source, mini-circuits mixer, amplifier

and 70 MHz band pass filter provided in the Demo accessory kit housed in the front panel of the ESA.

Note (1): In the following keystrokes, {} = soft key and [ ] = hard key.

Note (2): Optional settings are in smaller Italic font for your information.

Lets proceed with providing one of the sources of data required for the Noise Figure Calculation shown in

equation 1, The ENR Data.

Entering the ENR table for a noise source manually or automatically:

The noise source used for this demonstration is the N4002A smart noise source. This noise source has a

calibrated range of 10 MHz to 26.5 GHz. The SNS series broadband noise sources work with the ESA-E

series to simplify measurement set-up and improve accuracy. Only available with Agilent instruments, they

provide the following advantages.

Automatic download of Excess Noise Ratio (ENR) data to the ESA, speeding overall setuptime.

Electronic storage of ENR calibration data which all but eliminates the opportunity for user

error Automatic sensing of the ambient temperature of the measurement environment allowing the

ESA to compensate for these changes during the measurement cycle increasing the accuracy and

reliability of noise figure measurements.

Agilent is always sensitive to conservation of investment and so also provides an interface [+28V (pulsed)

noise source drive output] for the large installed base of 346 series noise sources. These noise sources do

not operate automatically as do the SNS Series, however, they are available with disks containing the noise

source ENR data which facilitates the process.

Figure 2: N4002A SNS Series

Noise Source available with

Agilent instruments only


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The ESA allows you to set the preference for which noise source drive output you want to use. Once

calibration data is entered into the measurement personality, system calibration and DUT measurements

can be made. In most cases a common ENR table can be used for calibration and measurements, however,

in the case of mixers, for example, the frequency range of the source for measurements may be outside the

range for calibration, and therefore two sources are required. This is an instance where the calibration ENR

table will be different from the measurement ENR table, so the common table function is turned off.

Step 1: Preferred step with Smart noise source.

Instructions: ESA-E series Spectrum

Analyzer

Keystrokes: ESA-E series Spectrum

Analyzer

Connect the SNS to the ESA using the 11730A

cable.

No key presses are required for this step.

It is important to note, though that the SNS

should not be disconnected while the upload

process is ongoing

Automatic upload of ENR data from SNS Series

noise source

[Meas Setup]{ENR}{SNS Setup}{Preferences

Norm SNS} Toggles to SNS if on Norm.

{Auto Load ENR} On Off Toggles to On if Off.

Verify that the data has correctly transferred over [Return]{Meas & Cal Table}

Simply connect the N4002A smart noise source to the ESA noise source output. using a 11730A cable to

automatically transfer the ENR data to the NFA. This simplifies the process and reduces the possibility

of user error due to incorrect entry.

Figure 3: Automatic upload of ENR data from SNS EEPROM


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Figure 4: Common ENR Table with ENR data for N4002A smart noise source

If the noise source preference was a normal 346 Series noise source, then this is the same interface that

you could have used to either enter the ENR data. The 346 Series come with a disk containing the noise

source ENR data. Load it as follows.

Instructions: ESA-E series Spectrum Analyzer Keystrokes: ESA-E series Spectrum Analyzer

Load the ENR numbers from disk

Change directory to A:\ if not already selected

[File]{Load}{Type}{More 1 of 3}{ENR

Meas/Common Table}

{Dir Select}, use [] or [] arrows to select driveA for the floppy then press {Dir Select}.

Highlight the ENR file name using [] or []andthen press {Load Now}

If you misplace the disks, you can enter the ENR

values manually from annotation on the Noise

source as follows. Add Excess Noise Ratio (ENR)

serial number and model number

{Meas Setup}, {ENR}, {Meas & Cal Table}

[Enter]{Serial #}.

Use the numeric pad and alpha editor to enter the

serial number

{model ID} and enter the model number using the

alpha editor and numeric key pad

Adding ENR values versus frequency

The table auto sorts by frequency

Press {Index} 1, {Frequency} 10 {MHz}, {ENR

Value}, 13.14 {dB}. Repeat the process for index 2

and so on.


Analyzer


AnalyzerSaving the calibration data to a floppy or the

internal memory of the ESAPress [File], {Save}, {Dir Select}, use [] or [] toselect the drive A for the floppy, then press {Dir

Select}.

Press {Type}{More 1 of 3}{ENR Meas/Common

Table}

Press {Name} and use the Alpha Editor to name the

file. When finished entering the name, press

[Return] and {Save Now}.


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Noise figure measurement process summary

Measuring the noise figure of a device also requires knowledge of the measurement

system. Once the noise figure of the measurement instrument is known and the gain of

the device under test (DUT) is known, then the noise figure of DUT can be calculated,

after the overall noise figure is measured.1. Enter the excess noise ratio ENR values in dB of the noise source. (Done)2. Calibrate the measurement personality.3. Make the Noise figure measurement using the Y-Factor method described above

in equation 3.

Model the measurement system as another stage with its own noise figure and gain

So during calibration we make a measurement on just Stage 2, which is the measurement system connected

to the D.U.T. This will allow us to measure F2 as in equation 3. After that, we also measure F12 , which is

the noise figure of the cascade. Finally, we need to determine the gain of the D.U.T. which will allow us to

report the noise figure of the D.U.T., by itself. This is done as described infigure 8: Theory refresh 3.First

lets proceed with the calibration .

F12 (Noise Figure)kToBGG

GkToBGGNaNakToBGG

No

NoSiGG

kToB

Si

NoSo

Ni

Si

21

21212

2121

++===

Na1 = kTe1G1B =kTo(F1-1)G1B and Na2 = kTe2G2B =kTo(F2-1)G2 B from equation 2

F12 (Noise Figure) =kToBGG

GkToBGGB1)G-kTo(FB1)G-kTo(F

21

2121122 ++ =kToBGG

11F)G

1-F(GkToBG

21

11

221

++

F12 (Noise Figure) = 11

2 F)G

1-F( +

1

21

G

1-FF + (4)

Hence F1 (Noise Figure) =

1

212

G

1-FF (5) Fig 5: Theory refresher 2

kToBkToBG1

Na1

kToBG1G2

B G1 Na1

Input

Noise

kToB

B, G2,Na2

Si SiG1 SiG1G2F1 F2

Na1G2

Na2Total

Noise

Added

Total

Noise

Power

Out ut

F12

Sta e 1

Stage 2


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Lab 2: Calibration of the noise figure measurement personality and HW (Opt. 219)

For accurate and correct measurements of noise figure for a DUT, the system must first be calibrated.

Calibration is required because the measurement system has its inherent noise figure that must be known

and corrected for before a DUT can be measured as shown above.

Following is the calibration process:

1: Select the frequency range appropriate for the D.U.T.

2: Set the number of points and set the number of averages.Any jitter in the calibration step will add to the

measurement uncertainty of all subsequent measurements. Therefore a long averaging time should be

used for calibration in order to reduce this source of uncertainty to a negligible level.3: If the device under test does not have gain or if the gain is low then it is recommended to have the built-

in preamplifier on before calibration.

Now Perform a system calibration

Instructions: ESA-E series Spectrum Analyzer Keystrokes: ESA-E series SpectrumAnalyzer

Access the DUT Setup diagram to obtain guidance onhow to setup connections for calibration of an amplifier

as a DUT.Press the tab keys to navigate your way around the form.

When the form Highlights the diagram field"Blue" you

should use the softkey to change the parameter.

[Mode Setup]{DUT Setup.}

{Calibration}

Connect the SNS to the ESA input connector as described

by the diagram for an amplifier

No key presses are required for this step.


Analyzer


Analyzer

Set the start frequency [Frequency] {Start Freq}, 10 MHz

Set the stop frequency [Frequency] {Stop Freq}, 3 GHz

Set the number of points at which to measure [Frequency] {Points}, 30 {enter}

Figure 6: Device under test

setup form. The DUT setupform allows the user to

prepare the DLP for

measuring specific devices

and setups, and provides

information on how to setup

the instrumentation for either

calibration as show above or

measurement.


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Set the averaging function to 15 averages [Meas Setup] {Avg Number On} 15 {Enter}

Calibrate the measurement personality [Meas Setup] {Calibrate} {Calibrate}

While the analyzer is calibrating, a quick refresher on how gain is measured

G1(D.U.T)

=)CAL(Gradient

)MEAS(Gradient=

CcalHcal

1cal2cal

CtotHtot

1tot2tot

T-T

N-N

T-T

N-N

(6)

Figure 7: Calibration process

on ESA. The ESA is set to

sweep a number of times(defined by averaging) across

the user defined frequency

range, cycling through all the

defined attenuator settings to

ensure that a corrected noise

figure measurement can be

made.

Since we are switching the same noise source between the same Thot and Tcold

during calibration and measurement, make THtot =THcal and TCtot=TCcal

G1(D.U.T) =1cal2cal

1tot2tot

N-N

N-N(7) Figure 8: Theory refresh 3.

N1cal

Nacal

N2cal

TsTH calTc cal

Calibration(Measurement System)

Output Noise Power

N1tot

Natot

N2tot

TsTH totTc tot

DUT Measurement(DUT & System)

Gradient =CcalHcal

1cal2cal

T-TN-N

=

CcalHcal

2ccal2hcal

T-T

BGkT-BGkT

=

CcalHcal

ccalhcal2

T-T

)T-(TkBG

Gradient(CAL) = kBG2

Gradient =CtotHtot

1tot2tot

T-TN-N

=

CtotHtot

21ctot21htot

T-T

GBGT-GBGkT

=

CtotHtot

ctothtot21

T-T

)T-(TGkBG

Gradient(MEAS = kBG1G2


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Equation 7 is the ratio of difference in output noise power measured with noise source on/off for

calibration and measurement setups.

Lab 3: Noise figure and gain measurements

Now that the measurement personality is calibrated with the noise source connected directly to the input, it

is a simple matter to makecorrectednoise figure and gain measurements on a device. The calibration

indicator on the top of your screen has changed from a red uncorr to a green corr. With no D.U.Tconnected, both the Gain and Noise Figure are at ~ 0db as expected. This is because the analyzer is

displaying corrected results with the noise contribution of the measurement system removed. Since the

input is noise, there is invariably some variation, however considering that most D.U.Ts have gain, from

equation 5 (pg. 7), this value should become negligible

To see the second stage noise figure (F2) that has been calibrated out, proceed as follows.


Analyzer


Analyzer

You can reduce averaging or turn it off for a

faster measurement

Setup an uncorrected display to display the

approximate noise figure of the measurement

system

[Meas Setup]{Avg On Off}

[Input/Output] {Noise figure Corrections}{Noise

figure Corrections On Off}

Figure 9: Corrected NF Gain

measurement after calibration


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Analyzer


AnalyzerToggle back to making a corrected measurement to

proceed with rest of lab.

[Input/Output] {Noise figure Corrections}{Noise

figure Corrections On Off}

Disconnect the noise source from the input and connect the device under test to the input and connect the

noise source to the DUT as shown in figure below.

Figure 11: Device under test setup form for an amplifier measurement.

As soon as the DUT is connected to the ESA, a measurement will begin on the noise figure and gain of the

amplifier because the system is already sweeping. The user has the flexibility to select single or continuous

sweep based on what the intention is. Additionally, the user can specify a lower number of averages to

permit a faster measurement.

Access this menu by pressing

[Mode Setup]{DUT Setup.}Press the tab keys to navigate

your way around the form.

When the form Highlights the

diagram field"Blue" you

should use the softkey to

change the parameter to

Measurement

Figure 10: Uncorrected

measurement, showing the

approximate NF of the

measurement system.


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Using the display featuresThe noise figure measurement personality has many features to help you interpret and analyze noise figure

measurements.

Perform display scaling



Restart the measurement if necessary

Expand the trace to fit the graph for a better view of

the measurement using the Auto Scale function as

shown in figure below.

Press [ESC] or [Return] to get out of DUT Setup

screen.

{Restart} for a faster response after changing DUT.

Press [Amplitude] use [Next Window] to highlight

the graph to be expanded then press {Auto Scale}

Figure 12: Display of Noise figure and gain after auto scaling

Manually configure your display via the AMPLITUDE key as follows..


Analyzer

Keystrokes: ESA-E series Spectrum Analyzer

Set the scale of the graphical view. Press [Next Window] to highlight the graph to be

changed. In this case the Gain window.

Press {Scale/Div} and enter the new value 2 {dB}

Set the reference value

Set the position of the reference.

Press [Amplitude] {Ref Value} and enter the value 20

and press dB

Move the position of the Reference Value by toggling

through {Ref Position Ctr}. Notice what happens

More Display Features.

Select and Zoom Active Window:

This feature allows you to highlight a window and then enlarge it for closer analysis.

Scale and reference levelvaluesThe scale in dB per division and the

reference values can be adjusted to

give an optimized view of the

measured results. The scale per

division can be adjusted from 0 to 20

dB. The Reference level can be placed

at the top of the graph, in the center or

at the bottom. The reference level is

also adjustable from 100 dB to +100

dB.

Use the Auto Scale feature to give thebroadest view of the measured trace.

The lowest point will be placed at the

bottom of the graph and the highest


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Highlight the window of interest Press [Next Window] until the window you want is

highlighted

Enlarge the window for closer analysis Press [Zoom]

Switch to another window (figure 13) Press [Next Window]

Figure 13: Full screen display of Noise figure and device gain

General, Markers and Source tabs

There are three tabs available at the bottom of the screen. These tabs are accessed using the [ ] and []tab arrow keys on the front panel of the ESA. The General tab shows information about BW, number of

points, Tcold value, loss, attenuator setting and internal preamplifier setting.

The Marker tab gives the frequency, noise figure and gain at each of the marker readings. The Source tab

has information about the noise source including serial number and model identification.


Analyzer


Analyzer

View the General table at the bottom of display. Use the Right and Left Tab keys at the bottom of

the front panel to scroll through the tabsView the Source tab at the bottom of the display. Use the Right and Left Tab keys.

Figure 14: General information display

Figure 15: Noise source information: Cal information is blank because user selected common ENR table

Markers


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A total of four normal markers can be placed on the graphical display. The placement of the markers is

limited to the number of equally spaced calibration points. For example, if there are 11 calibration points

then the markers can be placed on each of the vertical graticule lines. Each of the normal markers can be

changed to delta markers. For example marker 2 will change to marker 2 and 2R where 2R is the reference

and 2 would be the delta.



The marker function operates the same as the

standard ESA-E Series.

To turn marker on, press [Marker].

Turn on marker 2 Press {Select Marker 2} and press {Normal}

Active delta marker 2.

The marker table under the graphical display

reflects the delta marker information.

First place the marker to a reference point using

knob or up/down arrows. Press {Delta}. Move the

marker relative to the reference marker.

Switch between displaying the absolute frequency

of the delta marker and the reference marker

frequency.

Press {Delta Pair}. Note the change in frequency

above the graphical display.

Note that it is not necessary to toggle to the marker tab when selecting marker functions. This is

automatically displayed. Additionally, the analyzer toggles to the general tab once markers are turned off.

Change format of the active window

The default view of the window is the graphical mode with noise figure in the top and gain in the bottom.The two graphs can be combined to display both traces on one graph. There are two other views available;

the table mode, which some users prefer, and meter mode which provides quick and easy to read

measurement information while facilitating testing.


Analyzer


Analyzer

To combine both traces on one graph, see figure

below.

Press [View/ Trace]{Combined on}.

Figure 16: Display of markers

and delta markers on the ESA

allow noise figure and gain to

be read along the entire sweep


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Activate the table mode, see figure below Press [View/ Trace]{Table}

Activate the meter mode Press [View/ Trace]{Meter}

Change the measurement result you are displayingThe default display of the ESA is noise figure and gain., however there is a separate facility for displaying

6 different types of measurement results. This can be done independently for the two windows. Depending

on which one is chosen



Activate the table mode, see figure below Press [View/ Trace]{Result A}{Teffective}

Scale the view appropriately Press [Amplitude]{Auto Scale}

Figure 17: Different measurement result type on ESA.

Creating and testing to limit lines

In the manufacturing environment, it may be necessary to increase manufacturing through-put. This could

be implemented by inserting pass/fail limit lines. By using this function, the operator can quickly and

Figure 17: Combined display mode on the ESA and Table display mode on ESA.

Teffective from equation 2 is

proportional to noise figure and so the

graph should follow a similar trend


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efficiently quantify noise figure and gain dramatically reducing the time spent testing each DUT. Up to four

limit lines can be setup two for the upper graph and two for the lower graph. The two limit lines for the

upper graph are designated with up arrows (soft keys), and the limit lines for the lower graph are designated

with down arrows (soft keys). The limit lines can be designated as upper limit or lower limit and each can

have a test pass/fail indicator.



Change view back to default noise figure Press [View/Trace]{Result A}{Noise

Figure}{Noise Figure(dB)}

Open the limit line editor, select upper limit for the

upper graph and turn on the limit test.[Display]{limits}{limit 1}{Edit}, use [][] tabkeys under display to highlight Limit. Press {On},

move to Type, press {Upper}, move to Display

{On}, move to Test {On}.

Insert limit values for 10 MHz, 100MHz, 1, 2 and 3

GHz

Limit lines values take on the value of the set of

results it is being applied to.

Use [][] tab keys to highlight point 1. Press{Frequency 10 MHz}, {limit Value}[3]{ x 1},

{Connected Yes}, {Point 2} {Frequency 100

MHz}, {Limit Value}[ 4]{ x 1}, {Connected Yes},

{Point 3},{Frequency 1 GHz}, {Limit Value{[ 5]{

x 1}, {Connected Yes}, {Point 4},{Frequency 2GHz}, {Limit Value}[{ 5]{ x 1}, {Connected

Yes},{Point 5},{Frequency 3 GHz}, {Limit

Value}[ 8]{ x 1}, {Connected Yes}.

Figure 18:Limit line editor on the ESA.


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Figure 19: Measurement with limit test on, showing a passing noise figure limit test

Lab 4: Noise Figure Uncertainty Calculator

Option 219, noise figure personality has a built-in uncertainty calculator. To calculate the overall

measurement uncertainty, simply choose the default noise source (N4002A for example), enter the input

and output match of the device under test and the gain/noise figure of the DUT from the measurement

display and the value of the uncertainty will be calculated. There are some default values for the instrument(ESA) already entered.

Using the built-in uncertainty calculator to measure the uncertainty of the measurement for:


Analyzer


Select uncertainty calculator Press [Mode Setup], {Uncertainty Calculator}

Choose N4002A as the noise source Use [] [] tab keys to highlight Noise SourceModel box. Press {N4002A}

Setup the instrument NF and Gain uncertainty for

ENR and frequency range of measurement.

Instrument noise figure ~ what you saw in lab 3

during uncorrected measurement after calibration

Use [] [] tab keys to highlightInstrument Noise Figure and enter 8dB.

Highlight Noise figure uncertainty and enter 0.41 dB

Highlight Gain uncertainty and enter 0-.83 dB

Enter the Noise Figure and Gain values from the Using tab keys to highlight DUT Noise Figure and

Example:Frequency 525 MHz

D.U.T. with 24.85 dB gain

D.U.T. NF: 3.45 dB

N4002A ENR (12 16 dB) F


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measurements graph or marker table enter 3.45 dB. (To view the marker table, press

[Return] and to return to the calculator press

{Uncertainty Calculator}.

Then highlight DUT Gain and enter 24.45 dB.

The input and output match of the DUT is

determined from the specifications sheet or

measured using a network analyzer.

Highlight DUT Input Match and enter 1.5, Highlight

DUT Output Match and enter 1.5.

The measurement Uncertainty is then calculated and

the results is display at the bottom of the form.

SNS allows easy correction for physical temperature

While on uncertainty.

Remember from figure 1, page 3:

ENR= )Tc

TcTh(

: We assumed that Ts=Tc=To

The default value for Tcold used in the ESA is 296.5K. This is assumed to be the value of the noise source

physical temperature when in the off condition. The ENR vs frequency tables, characterizing each noise

source that was entered in Lab 1 are referenced to this. This may very well not be the case and if Tcold is

not 296.5K, the ENR will not be correct leading to an error in the noise figure measurement shown below.

Figure 20: Uncertainty

calculator display showing

result for the example above.

If you have the time, you can

observe the trends of

uncertainty changes, i.e.

increase in uncertainty as the

gain decreases etc


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19

Figure 21: Magnitude of error in noise figure measurement if true Tcold is not what the instrument expects

For a D.U.T. NF of 3.5 dB, and a temp error of 8K, there is almost an additional 0.1 dB that needs to be

added to the overall uncertainty budget!

This is why the SNS on the ESA is so valuable. They allow automatic sensing of the ambient temperature

of the measurement environment allowing the ESA to compensate for these changes during the

measurement cycle increasing the accuracy and reliability of noise figure measurements.



Automatic temperature sensing of Smart Noise

Source

[Meas Setup] {ENR}{Tcold}{Preferences Norm SNS}

Note that the SNS Tcold is ON. Because of this, the

Tcold reported in the general tab is not the Default of

296.5K. It is the automatically sensed ambient

temperature of 307.15K

Use the default Tcold value {SNS Tcold On Off}{User Tcold Default User}

You can also define your own Tcold, or sense

this from the SNS instantaneously

{User Tcold Default User}{User Tcold from SNS}


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Lab 5: Noise figure measurements using a mixer as the DUT

When a down conversion is included in the noise figure measurement, for example measuring the noisefigure of a mixer, there are some additional setups to consider. For this example let us use a mixer as a

downconverter with an IF at 70MHz, LO at 3GHZ and both RF sidebands are used, 2930 and 3070MHz i.e.

a DSB measurement.

The measurement as well as calibration is made at the IF frequency.

When an IF frequency is chosen, it is a good idea to keep the frequency as low as possible in orderto avoid large differences in ENR values between the upper and lower sidebands when using DSB

mode. This is because it is the ENR value at the LO that is used in the measurement (compromise

since it is centered between the 2 sidebands)

Since this device has some loss, it is recommended that the internal preamp be used.

Compensate for two sidebands by selecting double side band.

Any broadband noise in the LO will directly affect results. This can be solved by either a high passor low pass filter at the LO port that removes the noise at the IF frequency. Place an IF filter at the

input of the spectrum analyzer to remove LO feed through. Usually mixers have around 20dB ofisolation between the LO-IF port so the high powered LO will seriously affect results.

Disconnect the amplifier from the ESA



Setup the ESA for down conversion measurements

as shown in the diagrams below.

It is recommended that the internal preamp be used

when measuring devices that have low gain.

Press {Meas Setup} {More 1 of 2} {Restore Meas

Defaults}

Press {Meas Setup} {Int Preamp On Off}

Press [Mode Setup] {DUT Setup}{Down Conv}

Setup the LO frequency (figure 23) on the ESA Move to Ext LO frequency using tab keys the

enter 3GHz

Tab to Sideband and choose DSBSetup the fixed IF frequency [Frequency] {Freq mode}{Fixed}{Fixed

frequency}{70 MHz}

Calibration: connect the noise source to the input

of the ESA.

Press [Meas setup]{Calibrate}{Calibrate}

Figure 22: Automatic

sensing of ambient

temperature or user

definable Tcold..


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Measure the DUT: Connect the mixer IF (I) port to

the ESA, the LO (L) port to the signal source and

the RF (R) to the noise source.

To add more averaging, press [Meas Setup] then

{Avg Number On)

Instructions: ESGC E4438C Vector Signalgenerator

Keystrokes: ESG E4438C Vector Signalgenerator

Setup the source for + 7 dBm at 3 GHz On E4438C press [Frequency][ 3] GHz

[Amplitude] [7]{dBm}[RF On]


Analyzer


Analyzer

Change the ESA display to meter mode, more

appropriate for a single frequency measurment

[View/Trace]{Meter}

Figure 23: Setup for measuring

a down-convertor (mixer) at a

fixed LO and fixed IF

Figure 24: The meter view

showing noise figure and

Gain (conversion loss) of a


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The measurement is valid for a DSB device under test, provided that there isnt too much variation of the

frequency response of the D.U.T. and the ESA. This measurement could be used to estimate the SSB noise

figure without having to worry much about image reject filtering. The next page outlines the differences

and how one can correct for this. The details of mixer measurements are out of the scope of this lab.

For a S.S.B application, the analyzer should see the image frequency from just one sideband. So as a result,if the analyzer is using the D.S.B. measurement to approximate the S.S.B case, it will see the gain as twice

what it should be. And since noise figure =(Noise power out)/(Gain * Noise power in}, the noise figure will

be of what it should be in the S.S.B case. So a loss compensation of 3dB (gain of 3 dB) needs to be

applied to make the S.S.B equivalent measurement.

Loss CompensationCompensate for losses before and after the DUT. These losses can be fixed or varied versus frequency. The

figures below shows the before and after setup menu. The before menu as well as the after can be

setup to have a table of losses versus frequency or a fixed value. For fixed values, input a value for loss in

dB and temperature in K. In our example, lets use a fixed gain (negative loss) after the DUT since we are

making a fixed frequency measurement.


Analyzer


Enter a fixed loss value to use as compensation

after the DUT

Press [Input/Output], {Loss Comp}and {Setup}. Use

the tab keys under the display to highlight the box

labeled {Loss Compensation after DUT} and press

{fixed}. Tab to {Fixed Value} and enter 3 dB.

The temperature of the loss must also be entered.

In this case room temperature.

Tab to {Temperature} in the before box and enter

290 K

The loss compensation could also have been setup vs frequency in a tabular format

F LO

Fif

Noisepower

Freq

LSB

USB

Measurementfrequency (IF)

For D.S.B. measurement1) During Calibration, the analyzer

uses ENR values at I.F. frequency

2) During measurement, the analyzer

uses the average of the U.S.B. and

L.S.B. ENR valuesFif

0


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Figure 25: Loss Compensation selection table Noise figure after loss compensation

Narrowband noise figure measurementsThe noise figure measurement personality has the capability to reduce the resolution bandwidth allowing

narrow bandwidth measurements. As the bandwidth narrows, the measurement jitter increases. It is

recommended that the number of averages increase to reduce the jitter. In this measurement, the deviceunder test will be an amplifier, band limited, with a band pass filter which has a center frequency of 70

MHz. The start and stop frequencies are set and the number of points to be measured are set. In this

example 30 points will be used. The figure below is an example of a narrowband measurement.



Setup the ESA for narrow band measurements. Press [Mode Setup] {DUT Setup}{Amplifier}

Connect the noise source directly to the spectrum

analyzer

ESA-E SeriesSpectrum

Top of unit front panel

Smart NoiseSource

N-TYPE TO SMAAMP

SMA TO SMAAmp. Power

Mini CircuitsFilter

Mini Circuits Amplifier

11730 SNS cable

SNS output

connector

Figure 26: Connection

diagram for narrow band

measurements


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N i Fi L b S800 N b 2003 24

Set start and stop frequency [Frequency]{Freq Mode Swept}{Start Freq, 50

MHz}{Stop Freq, 90 MHz}

Set the number of measurement points [Frequency]{Points} 30 enter

Set the resolution bandwidth [BW/Avg], 300 kHz

To reduce measurement jitter add averaging then

calibrate

[Meas Setup]{Avg Number}15{Enter},

{Calibrate}{Calibrate}

To measure the DUT connect the filter to the noisesource and the other end to the input of the amplifier

and the output of the amplifier to SA input.

To achieve the display shown below [Trace/View], {Combined On}

[Amplitude]{Auto Scale}

Figure 25: Narrow band measurements display of filter in cascade with amplifier.

s800NFSA Noise Lna

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